1. Technical Field
The present invention relates in general to manufacturing glass articles and, in particular, to an improved system, method, and apparatus for an adjustable stacker bar assembly for hot glass article fabrication operation.
2. Description of the Related Art
To fabricate a glass article, a mass of molten glass is typically blown into a mold, partially cooled, and the resultant hot glass article transferred to an annealing oven. During transfer to the annealing oven, the hot glass articles are extremely fragile and susceptible to thermal and physical stress, contamination, and other damage. In addition, annealing or other post-forming process steps may not fully remove added stress concentrations or risers and other defects in the hot glass articles caused by the handling fixtures or transfer equipment.
Any fixtures or equipment touched by hot unannealed glass articles should be made of materials that will minimize stress concentration, contamination, deformation, cracking, or checking of the hot glass. Furthermore, the materials used to handle the hot glass articles must themselves be able to withstand the high temperature contact with the hot glass articles and be rigid enough to insure proper alignment/placement of the articles within the annealing oven.
Stainless steel and other high temperature metal alloys have been used for the body or support structure of fixtures that handle hot glass articles. However, metallic materials can cause thermal and/or physical damage if they contact hot glass articles. Therefore, various nonmetallic contact materials have typically been incorporated into fixture designs as removable inserts, pads, or spacers for contacting the hot glass articles, e.g., fabric cloth coverings capable of withstanding high temperatures) or asbestos, plastics, and graphite-containing pads attached to a steel support bar. Unfortunately, the use of these nonmetallic materials presents drawbacks to glass manufacturers.
Although asbestos may have very good thermal and physical properties for this application, its use creates grave environmental and workplace safety concerns. Plastics are generally less well suited for this high temperature application and typically have a relatively short service life even when specially formulated to withstand the high temperatures encountered in this hot end process. Graphite may be more of an ideal nonmetallic material for handling hot glass since graphite has resistance to oxidation at temperatures typically encountered when contacting hot glass articles, nonabrasive surface integrity, and acceptable heat resistance. It is also safe for the environment and to those who work with it.
However, graphite presents several problems that must be overcome before it can be economically used as a material for handling hot glass articles. One problem graphite presents is that it is relatively brittle and therefore can chip or crack or be otherwise mechanically damaged. Another problem frequently encountered with graphite is the difficulty in removably attaching a graphite contact pad to the supporting body of a fixture. Since graphite can wear during use, the graphite contact material should be readily removable. Removability can result in the attachment to the supporting structure not holding the graphite rigidly and reliably during glass production. Another problem is the need to economically provide an array of graphite contact pads in different shapes and sizes to handle different shapes and sizes of hot glass articles, e.g., the need for machinability.
One specific device for handling hot gas articles is a stacker bar assembly that typically uses nonmetallic pads. Such an assembly is typically used to transfer glassware from a narrow, single line conveyer, known as a cross conveyor, across a transfer plate to a multi-line conveyor. The stacker bar assembly may impart motion in several directions, e.g., to properly space hot glass articles in the oven as well as push the articles into the oven.
A typical stacker bar assembly is composed of a steel support tubing, and a glass contact surface, such as attached fabric or carbon-based pads. The assembly typically forms pockets for a particular shape and size of glassware. Thus, many stacker bar assemblies are required to handle the needs of a typical glassware manufacturing facility producing different shapes and sizes of glass articles.
Handling and other problems resulting from graphite's brittleness and relatively short life (when compared to high temperature metallic components), difficulties in rigidly attaching a brittle, low strength material to the steel support, and machining difficulties make graphite, composite graphite, and other carbon materials difficult to use as a contact material in stacker bar assemblies. Graphite or carbon materials can be combined with plastic resins or fibers, but resins and reinforcing fibers create new problems. The resins typically have limited thermal capability, and fiber reinforced compositions are typically not easily machinable, making fabrication of some complex shapes difficult if not impossible. Frequent removal of pads to adapt to different glass articles sizes also increases the risk of damage.
Currently, fabricators of glass articles select stacker bar assemblies based on many different variables, such as worker skill level, the number of different sizes of containers to produce, personal preference, etc. In the prior art, U.S. Pat. No. 5,741,343 discloses one type of an adjustable hot glass transfer device. This device uses repositionable stacker bar pads formed from a nonmetallic material. The pads have tongue-in-groove adjoining surfaces and glass contact surfaces that are serrated. This pads also have a rough finish to minimize thermal checking and other hot glass article problems. Although this design offers a workable solution, it can be time consuming to adjust the pads to glass articles of differing size, and/or to replace worn or damaged pads. Thus, an improved solution would be desirable.